The present invention relates to printed media production and in particular ink jet printers.
Ink jet printers are a well known and widely used form of printed media production. Ink is fed to an array of micro-processor controlled nozzles on a printhead. As the print head passes over the media, ink is ejected from the array of nozzles to produce an image on the media.
Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters.
Recently, the array of nozzles has been formed using microelectromechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picolitre (xc3x9710xe2x88x9212 liter) range.
While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may misdirect the ejected drops or simply fail to eject the ink at all. If the nozzle fails to eject the ink, it can start to bead and affect surrounding nozzles. In time, it may also leak ink onto the printed substrate.
Whether the ejected ink is misdirected or the ink beads on the surface of the printhead, both situations are detrimental to print quality. To address this, the printhead can be provided with an apertured guard over the exterior of the nozzles to avoid damaging contact fingers, dust or the media. However, the guard may also be used to retain misdirected ink droplets or any ink leaked from damaged nozzles. By localizing any ink leakage, the number of nozzles affected can be limited. The guard also prevents misdirected ink droplets from reaching the media.
Unfortunately, the print quality still suffers because it no longer includes the ink from the damaged nozzles. Furthermore, as the containment formation fills with ink, it can still bead on the exterior of the guard to clog the surrounding apertures and or leak onto the media.
Accordingly, the present invention provides a printhead for an ink jet printer, the printhead including:
a substrate carrying an array of nozzles for ejecting ink onto media to be printed;
an apertured guard positioned over at least one of the nozzles such that ejected ink passes through an aperture and onto the media;
the guard and the nozzle at least partially defining a containment formation for isolating leaked or misdirected ink from the nozzle from at least some of the other nozzles in the array; and
means to detect a predetermined amount of ink in the containment formation and stop further supply of ink to the nozzle.
In this specification the term xe2x80x9cnozzlexe2x80x9d is to be understood as an element defining an opening and not the opening itself.
Preferably, each nozzle in the array has a respective containment formation to isolate it from all the other nozzles in the array and each of the containment formations has one of said detection means. However, some forms of the invention may have a containment formation configured for isolating predetermined groups of nozzles from the other nozzles in the array; wherein
the detection means associated with each of the containment formations is configured to stop further supply of ink to the predetermined group upon sensing a predetermined level of ink in the containment formation.
In one form, each of the nozzles use a bend actuator attached to a paddle for ejecting ink wherein the detection means disables the bend actuator to stop further supply of ink to the nozzle.
In a preferred form, the detection means has a pair of electrical contacts positioned in the containment formation such that an accumulation of the predetermined amount of ink closes an electrical circuit such that a comparator disables the actuator.
In some embodiments, the containment formation further includes containment walls extending from the guard to the exterior of each of the nozzles. In a further preferred form, the nozzle guard is formed from silicon.
In one particularly preferred form, the detection means provides feedback for a fault tolerance facility to adjust the operation of other nozzles with the array to compensate for the damaged nozzle.
An ink jet printer printhead according to the present invention, not only isolates any ink leakage such that it is contained to a single nozzle or group of nozzles, but senses the accumulation of ink and stops further supply to that nozzle or group of nozzles. This prevents the supply of ink to damaged nozzles to go unchecked.
The containment walls necessarily use up a proportion of the surface area of the printhead, and this adversely affects the nozzle packing density. The extra printhead chip area required can add 20% to the costs of manufacturing the chip. However, in situations where nozzle manufacture is unreliable, the present invention will maintain print quality despite a relatively high nozzle defect rate.
The nozzle guard may further include fluid inlet openings for directing fluid through the apertures to inhibit the build up of foreign particles on the nozzle array.
The fluid inlet openings may be positioned remote from a bond pad of the nozzle array.
By providing a nozzle guard for the printhead, the nozzle structures can be protected from being touched or bumped against most other surfaces. To optimize the protection provided, the guard forms a flat shield covering the exterior side of the nozzles and has an array of apertures big enough to allow the ejection of ink droplets but small enough to prevent inadvertent contact or the ingress of most dust particles. By forming the shield from silicon, its coefficient of thermal expansion substantially matches that of the nozzle array. This will help to prevent the array of apertures in the shield from falling out of register with the nozzle array as the printhead heats up to it operating temperature. Using silicon also allows the shield to be accurately micro-machined using MEMS techniques. Furthermore, silicon is very strong and substantially non-deformable.